Scientists see cure for colorblindness

University of Washington researchers Jay and Maureen Neitz, seen holding testing cards for color perception, have teamed up with a California biotech company for a prospective gene-therapy cure for colorblindness. (Ken Lambert/Seattle Times/TNS)
University of Washington researchers Jay and Maureen Neitz, seen holding testing cards for color perception, have teamed up with a California biotech company for a prospective gene-therapy cure for colorblindness. (Ken Lambert/Seattle Times/TNS)

For the more than 10 million Americans with colorblindness, there has never been a treatment, let alone a cure, for the condition that leaves them unable to distinguish certain hues.

Two University of Washington professors have teamed with a California biotech firm to develop what they say could be a solution: a single shot in the eye that reveals the world in full color.

The research has a long way to go, but Jay and Maureen Neitz, husband and wife, have already shown it's possible to apply gene therapy to correct the vision disorder in male squirrel monkeys.

They have arranged an exclusive license agreement between UW and Avalanche Biotechnologies of Menlo Park for a new way to deliver genes that can replace missing color-producing proteins in the eye cells called cones.

"I don't think there's any question that it will work," said Maureen Neitz, 57, a UW professor of ophthalmology.

The potential treatment -- which could be tested in humans within two years, assuming preparatory tests succeed -- would be a boon for the 1-in-12 men and 1-in-230 women with color-vision deficiency.

The trouble occurs when people are born without one or more of the three types of color-sensing proteins typically present in the cones of the human retina. The most common type is red-green colorblindness, followed by blue-yellow colorblindness. A very

small proportion of the population is completely colorblind, seeing only shades of gray.

Because they can't perceive certain colors, these people see hues in muted or different shades than people with more typical vision.

Colorblindness is often a genetic disorder. It affects mostly men, who can inherit a mutation on the X chromosome that impairs their perception of red and green. A much smaller fraction of cases are in women, who have two X chromosomes, which gives them a better chance of avoiding effects of any genetic defect.

GENE THERAPY

The Neitzes have focused on the disorder for years. Jay Neitz, 61, is a professor of ophthalmology. He confirmed in 1989 that dogs are colorblind, too.

The couple proved in 2009 they could use gene therapy to correct colorblindness in male squirrel monkeys, which are born unable to distinguish between red and green.

In the journal Nature, they reported the success of a technique that inserted the human form of a gene that detects red color into a viral shell, and then injected it behind the retinas of two squirrel monkeys.

The monkeys, named Sam and Dalton -- the latter after the British chemist John Dalton, who was the first to analyze and report on his color-vision deficiency -- had been trained to recognize colors on a computer screen in exchange for a reward of grape juice. Before the surgery, they couldn't detect certain hues, while after the procedure they got them right nearly every time.

But that technique is risky, requiring surgery, so the Neitzes were looking for another way to do the job.

LONG WAY TO GO

"For 10 years, we have been trying to figure out a way to get the genes to go to the back of the eye with a simple shot," Jay Neitz said.

With the help of Avalanche, the researchers say they've developed a technique that does just that. It uses a safe vector, called an adeno-associated virus, to house the pigment gene, which is injected directly into the vitreous, the jellylike center of the eye. Once there, it targets cells on the back of the retina, said Thomas W. Chalberg Jr., the co-founder and chief executive of the firm.

"It's a protein shell, kind of like a Trojan horse, that gets you entry into the cell. Once you're there, the DNA gets to set up shop and produce the photo pigment of interest," he said. Avalanche has two drug candidates, AVA-322 and AVA-323, that carry pigment-producing genes.

It takes only 30 percent of the cells to be transduced, or changed, to put the world in a whole new hue, Neitz said. Early tests show the technique meets that mark in monkeys.

After preclinical trials are complete, Chalberg said he hopes to move to human trials within one to two years and then seek federal Food and Drug Administration approval for the treatment. Eventually, the treatment could be offered during a single visit to an opthalmologist's office.

Such a development would be "an amazing advantage," said Dr. Rohit Varma, a professor of ophthalmology and director of the Eye Institute at the University of Southern California, who is not involved in the research.

"It would cure or at least help people who are colorblind," he said. "This is the first hope, in many ways, for these individuals who suffer from this."

While noting that many tests that succeeded in animals have later failed in humans, he said he's cautiously optimistic that the trials will deliver as promised. Plus, he said, it will be important to learn whether the therapy not only adds the color-sensing ability, but actually improves the lives of those who are treated.

That's a thought echoed by Dr. Paul Sternberg Jr., chairman of the Vanderbilt Eye Institute at Vanderbilt University in Nashville and a clinical spokesman for the American Academy of Ophthalmology.

He called the Neitzes "world-class scientists" and said the wider field awaits potential human trials of the technique.

"The brain develops a certain way of seeing," he said. "We don't know whether replacing the visual pigment in a 25-year-old colorblind man will allow him to see in full color."

Already there appears to be high interest in finding out. Since March 25, more than 10,000 people have visited a new website associated with the project, colorvisionawareness.com.

ActiveStyle on 04/20/2015

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